Hi, It seems that gdk-pixbuf 2.24 moved -lm to Libs.private, so tumbler fails to build because it doesn't link explicitly with it, although all plugins use rint(). Thanks. (unrelated, but you registered tumbler 1.2.23 in bugzilla, instead of 0.1.23, I guess ;-)
This should be fixed in master now, please re-open if this is not the case. commit 88507955ba898d4a53241c5d542137ca35c02aac Author: Jannis Pohlmann <jannis.pohlmann@codethink.co.uk> Date: Fri Feb 24 16:37:05 2012 +0000 Link all plugins that use rint() against libm (-lm).